The present invention relates to a method and apparatus for distinguishing cancerous tissue from benign tumor tissue, benign tissue or normal tissue and more particularly to a method and apparatus for distinguishing cancerous tissue from benign tumor tissue, benign tissue or normal tissue using native fluorescence. As used herein, the term "cancerous tissue" includes cancerous tumor tissue.
Because a sufficiently effective method has not yet been developed to prevent cancer, cancer research has focused primarily on the most effective ways to diagnose and treat cancer. As different as the various forms of treatment have been--ranging from excision to radiation to chemotherapy--all treatments have relied on one crucial step, detection of the tissue that is cancerous. The importance of detection cannot be stressed enough. Early detection not only indicates the presence of a cancer but also may give an indication as to where the cancer originated and as to what type of treatment will be the most safe and effective method. Early detection can provide such benefits because it reveals the state of maturation of the cancer cell. Cancer cells are clonal cells of a single "founder" cell that is the result of some mutation of the normal cell for the particular tissue. As a result of the mutation, the founder cell replicates and divides, eventually forming a mass of cells called a tumor. Cancerous tumors are harmful because they proliferate at a metabolic rate that exceeds that of the normal neighboring cells. As a result, the cancerous tumor grows at the expense of the normal neighboring tissue, ultimately destroying the normal tissue. One of the reasons why it is so difficult to completely cure cancer is that cancer cells have the ability to disseminate throughout the body via lymphatic or circulatory systems and to create new tumors where they arrive. However, this ability to disseminate comes only to those cells that have lost the characteristic membrane glycoproteins of the mutated tissue. For this reason, it takes a while before cancer can spread. An advantage to early detection is that the cells can be examined for characteristic properties such as cell size and shape to determine the source of the cancer cells.
It should be noted that in addition to tumors which are cancerous, there are tumors which are non-cancerous. Non-cancerous tumors are commonly referred to as benign tumors.
Clearly, the importance of an accurate technique that can be utilized either in vivo or in vitro for detecting cancerous tumors cannot be minimized. The advantage of an in vivo technique is that sensitive tissue may be tested, relatively undisturbed, for example, with the use of an inserted optical fiber probe. An article entitled, "Gastrointestinal Endoscopy" appearing in Clinical Symposia Vol. 32, Number 3 delineates the possible use for such a method of detecting cancer. As another example, an endoscope can be used to test tissue in vivo.
In copending U.S. patent application Ser. No. 186,747 filed on Apr. 25, 1988 in the name of Robert R. Alfano et al there is disclosed a method and apparatus for distinguishing between cancerous and normal tissue using native visible fluorescence. The technique involves exciting the tissue with a beam of monochromatic light having a wavelength of about 488 nanometers (nm) and then measuring the intensity of the fluorescence produced over a spectral region from about 500 to 700 nanometers.
Although the above technique is useful in distinguishing cancerous from normal tissue it does not distinguish cancerous tissue from benign tissue and benign tumor tissue. In some cases, samples of benign tissue and benign tumor tissue that have been tested using the technique produced spectral profiles similar to cancerous tissue or cancerous tumors and in other cases samples of benign tissue and benign tumor tissue produced spectral profiles similar to normal tissue using the above noted 488 excitation.
As can be appreciated, the key behind a spectroscopic technique for detecting cancer involves being able to distinguish between cancerous and benign tissue and benign tumor tissue as well as between cancerous and normal tissue.
In U.S. Pat. No. 4,718,417 to Kittrell et al there is disclosed a method of distinguishing artery wall from atherometous plaque or other material using visible fluorescence induced by 480 nm exciting light.
In U.S. Pat. No. 4,785,806 to L. I. Deckelbaum there is disclosed a method of ablating atherosclerotic tissue in which a fluorescence pattern of the tissue obtained by UV excitation is first examined to see if it is normal or abnormal.
Other known references of interest are U.S. Pat. No. 4,290,433 to Robert R. Alfano, U.S. Pat. No. 4,479,499 to Robert R. Alfano and U.S. Pat. No. 4,566,057 to T. Hiruma et al.